The reheat and stretch blow molding of plastic preforms or parisons sometimes requires that the preform be specifically located in relation to the blow mold so that the shape of the blown article is accurately registered. For example, the neck finish of the preform should desirably be properly located in relation to the blow mold, especially for non-symmetrical preforms, so that the shape of the blown article is correctly registered in relation to the neck finish, or thread start and/or finish portion of the article.
The apparatus described in U.S. Pat. No. 4,690,633 carries preforms on pallets from a loading station to a finishing or blowing station via a conditioning station. The preform is blown at the blowing station and then the blown article moved to an unloading station. Preforms of non-symmetrical shape can be transported by the pallets in this device; however, the preform must be properly positioned immediately prior to the blowing stage and the positioning must be maintained in the blowing stage so that the body shape of the blown article is correctly registered. In the above apparatus, the preforms are correctly located at the loading station since the preforms are removed from the injection molds using a robot and take off plate which directly places the preforms onto the mandrels in the loading station. Thereafter, the preform is firmly held by the mandrel throughout the preform's passage through the device. However, the mandrels spin during their passage through the conditioning station in order to impart the desired temperature conditions and this spinning changes the orientation of the preforms.
It is therefore, an object of the present invention to provide an apparatus which properly positions the preform prior to blowing and maintains the correct positioning at the blow station.
It is a still further object of the present invention to provide an apparatus as aforesaid which is suitable for use with non-symmetrical preforms and which is suitable for use with preforms held on mandrels which spin during a temperature conditioning cycle.
Further objects and advantages of the present invention will appear hereinbelow.